"Whether you like him or not, George Bush gave us Obama and I'm not happy about it, okay? I'm not happy about it. We have a disaster on our hands. We have a man, right now, that almost certainly will go down as the worst president in the history of the United States," Trump said.

Trump said he has put off agreeing to an extension of his "Celebrity Apprentice" TV show and that he will make an announcement on his campaign plans before June.